Pulse oximetry is a noninvasive method of continuously moni-toring the oxygen saturation of hemoglobin (SpO2 or SaO2). Al-though pulse oximetry does not replace arterial blood gas measurement, it is an effective tool to monitor for subtle or sud-den changes in oxygen saturation. It is used in all settings where oxygen saturation monitoring is needed, such as the home, clin-ics, ambulatory surgical settings, and hospitals.
A probe or sensor is attached to the fingertip (Fig. 21-14), forehead, earlobe, or bridge of the nose. The sensor detects changes in oxygen saturation levels by monitoring light signals generated by the oximeter and reflected by blood pulsing through the tissue at the probe. Normal SpO2 values are 95% to 100%. Values less than 85% indicate that the tissues are not receiving enough oxy-gen, and the patient needs further evaluation. SpO2 values ob-tained by pulse oximetry are unreliable in cardiac arrest and shock, when dyes (ie, methylene blue) or vasoconstrictor med-ications have been used, or when the patient has severe anemia or a high carbon monoxide level.
Throat cultures may be performed to identify organisms respon-sible for pharyngitis. Throat culture may also assist in identifying organisms responsible for infection of the lower respiratory tract. Nasal swabs also may be performed for the same purpose.
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